Laminates of aluminum, notably in the form of foil, and plastics resin films, such as polyethylenes, polyesters, polypropylenes and the like, are staple products of commerce. It is known, however, that aluminum does not present a completely satisfactory adhesive bonding surface for laminates for use in retort operations.
Problems which occur in adhesively bonded aluminum-plastics resin film laminates, especially with regard to aluminum foil laminates, is the formation of blisters or the delamination of the foil and film. This problem is likely to occur if the laminate is subjected to a retorting operation.
The retort procedure, as applied to a pouch formed from aluminum foil-plastics resin film laminates, comprises subjecting a filled pouch to a pressurized steam heating operation, with temperatures in the order of about 250.degree. F. It is in this operation that blisters and/or delamination most often is initiated.
The dry laminating of plastics resin films to aluminum, and more particularly aluminum foil, may take place in the following manner. A thermosetting or thermoplastic adhesive is applied to either the aluminum surface or the surface of the plastics resin film to be bonded and the aluminum or the plastics resin film having the adhesive thereon is heated to dry the adhesive. The aluminum surface and the film surface are then contacted, with the now dry adhesive therebetween, and passed between a pair of pressure rollers, at least one of which is heated, to soften the adhesive and complete the bonding operation.
It is desirable, therefore, to provide a pretreatment material for the aluminum surface to be bonded which reduces the tendency for blisters or delamination to occur in laminates formed from aluminum and plastics resin films, especially laminates formed from aluminum foils.